The present invention relates to a method for transferring data between two devices, and in particular, to a method for transmitting data from a first processing unit having a relatively large memory capacity to a second processing unit having a relatively small memory capacity. More specifically, the present invention pertains to a method for transmitting data from a first processing unit having a relatively large memory capacity to a second processing unit having a relatively small memory capacity, while the difference between the memory capacities of the two processing units is taken into consideration.
In accordance with recent technical progress, various personal computers (hereafter referred to as "PCs"), such as desktop and notebook types, have been developed and are available on the market.
As is well known, these PCs can be employed for many applications by executing application programs. Word processing software for editing documents and database software for calculation are very popular examples of such application programs. The forms of application programs vary, however, and lately programs have appeared that support user management of personal information: schedulers, telephone books/address books, and note pads. A so-called PIM (Personal Information Manager) is personal information management software that provides for the total management of personal data. With a PIM, a user can enter into a scheduler the name of a company for which a person that the user has contacted works, and when the name of that company is changed and the user enters the new name in an address book, an interactive function automatically changes the company name entry for the scheduler. "Lotus Organizer" is an example of such PIM software.
PC hardware comes in a variety of shapes. There is, for example, a PC card, the "ChipCard" (see FIG. 7), which is sold by IBM Japan, Co., Ltd., that conforms to the standard specifications established by PCMCIA/JEIDA. (PCMCIA/JEIDA: PCMCIA is an abbreviation of "Personal Computer Memory Card International Association", and JEIDA is an abbreviation of "Japan Electronic Industry Development Association". The PCMCIA and JEIDA work together for standardization of PC cards.) An important feature of this PC card, the design of which is based on the PC architecture and which incorporates a CPU, is that it can be used independently (stand-alone), while when it is inserted into a card slot of a PC (host machine) it serves as a memory card. A host machine into which a ChipCard is inserted can download to the ChipCard personal information (e.g., a calendar, schedule management data, time, a telephone book, and business card management data) that has been edited by the PIM software on the host machine, and can refer to and edit data that have accumulated on the ChipCard. When the ChipCard is removed from the card slot and is in the stand-alone state, however, its incorporated CPU functions independently, and the ChipCard can be used as an electronic notebook in which personal information that has been obtained by downloading can be referred to. Accordingly, data stored in the ChipCard can also be updated by employing a user interface provided for the ChipCard, i.e., a liquid crystal display panel and key pads.
The ChipCard, in other words, can function both as a memory card and as an electronic notebook, and was produced to enable data managed by a common PC (hereinafter referred to as a "host machine") to be also used in a mobile environment. A user can create a database on a host machine having a full-sized keyboard and a large screen display, and can temporarily save the created database on, for example, a hard disk in the host machine. The data can thereafter be transmitted to a ChipCard inserted into a PC card slot by using a download utility program. Therefore, so long as a user carries the ChipCard, he or she can refer to the data that are created by the PC, or can partially change that data, even in a mobile environment.
Although the main feature of a ChipCard is its compact and light "PC", this feature is accompanied by various trade-off problems.
One of the trade-offs is that its memory capacity is limited. A desktop PC or a notebook PC, for example, can easily acquire a memory capacity of several hundred MB or several GB by mounting a hard disk. On the other hand, because of size and weight limitations, available memory means for a ChipCard is limited to a memory chip, such as SRAM, which has only a small capacity (several hundred KB). In other words, the difference between the memory capacities of a host machine and a ChipCard can be great.
Since there is no limitation on the memory capacity of a host machine, a user can create a huge database by using database software. For example, a schedule management database (e.g., a diary or a To Do list) for several months, or spanning a period longer than a year, can be edited by using a PIM, such as Lotus Organizer, and the resultant data can be accumulated on the HDD. While, a ChipCard, which has only a small capacity, can spare only 100 KB for one application (e.g., schedule management software, such as a "data viewer"). If a data transmission utility program in a host machine does not take into consideration the difference in the memory capacities of the two devices, and transfers a huge amount of data to the card as it is, this may have unexpected consequences, such as the overwriting and destruction of other data existing in the memory device.